The present invention relates to a plating method, a plating device and a plating system. The present invention is suitable as a process in place of part or all of chemical mechanical polisher (CMP) step in a wafer planarization process in the manufacturing process of devices, such as copper(Cu)-wired devices.
In recent years, with a high densification and refinement in semiconductor products, the CMP process is being watched as a supplement of lithography having a shallow depth of focus with the progress of refinement. In the CMP method process, a chemical abrasive (slurry), a pad, etc. are used to mechanically polish the object for its planarization. In place of the glass-melting method and the spin-on glass method in the past, the CMP method has been expected as a technique suitable to the planarization process in case of forming a superfine pattern less than 1 xcexcm. Additionally, not only is the CMP method employed for the planarization, but also the CMP method is used to form an embedded wiring (damascene). The reason is that the wiring line can be formed with high accuracy by etching an oxidation film rather than etching a metal.
Meanwhile, this technical field is now investigating the next-coming wiring material capable of coping with high speed, high reliability and high integration in a semiconductor element. The use of copper (Cu) is now under review as a substitute of materials of aluminum (Al) alloy. The use of copper has an effect on the reduction of wiring resistance and wiring delay since copper (Cu) has a resistivity of the order of 60 per cent against the resistivity of aluminum (Al). Again, copper (Cu) has a high melting point and the copper""s life of an electro-migration is larger than that of aluminum (Al), on the order of about three figures with high reliability.
Since the steam pressure of copper is too high to form a pattern by normal etching, it is especially desirable to adopt the CMP method for the damascene process utilizing copper. The damascene process is effective in wiring in case of using a serious material in etching and has an effect to reduce the manufacturing cost which is apt to rise with an increase of wiring steps by multi-layer wiring. In the damascene process, a method allowing embedding the bier and forming the wiring line simultaneously is called as xe2x80x9cdual damascenexe2x80x9d particularly. According to the dual damascene, the wiring line and the bier (note: Contact hole is the general term for these elements in this specification, below.) are firstly dug in a layer insulating film. Subsequently, copper is embedded into the contact hole by an electrolytic plating method etc. After the formation of Cu film, superfluous copper besides copper embedded in the contact hole is eliminated for planarization by a Cu-CMP method.
However, the Cu-CMP method has a typical problem of over-polishing. This over-polishing means that a plating film of Cu is ground excessively and sometimes the over-polishing is explained by technical terms of xe2x80x9cdishingxe2x80x9d and xe2x80x9cerosionxe2x80x9d. With reference to FIG. 22, we now explain both dishing and erosion below. A wafer consists of an insulating film and a metal (film) 16 (16a and 16b). In the figure, reference numeral I designates an area having low wiring density, while II denotes another area having high wiring density.
In the area I of low wiring density, there is a dish-shaped depression formed in an embedded metal 16b due to the softness of a grinding pad, in spite of the presence of the insulating film 14 as a stopper against the grinding. This phenomenon is known as xe2x80x9cdishing xe2x80x9d in this field. On the other hand, in the area II of high wiring density, the insulating film 14 has not a strength becoming to the stopper because of its small area. Additionally, since the insulating film 14 differs from the metal 16 in terms of frictional coefficient against the grinding, it is also difficult to control the grinding process. As a result, the insulating film 14 is also ground together with the metal 16b. This phenomenon is known as xe2x80x9cerosionxe2x80x9d in this field.
The dishing can be lightened by using a pad of hard material or forming a dummy pattern in such the area having low wiring density. However, the pad being too hard is apt to produce fine scars (scratches) on the surface of the semiconductor, causing an inferior device. Therefore, it is difficult to select an appropriate material for the grinding pad. Although the erosion can be also reduced by the use of a pad of hard material, which is similar to the dishing, there is required a more careful control than that of the dishing. In this way, the over-polishing causes the deformation of wafer and the reduction in wafer thickness. Furthermore, the grinding of metal in the contact hole causes the increase of a wiring resistance or the snapping of a wire thereby to impede the manufacturing of high-quality semiconductor elements. For example, other explanations about both dishing and erosion are disclosed in pages 96 to 99 in the January issue of the Electric Journal published on 1999.
Under such a situation, an exemplified and omnibus object of the present invention is to provide a new and useful plating method, a plating device and a plating system embodying the method, all of which can solve the above-mentioned conventional problem.
Particularly, the exemplified object of the present invention is to provide a plating method which can offer the planarization treatment of high quality in comparison with the conventional plating method and also provide a plating device adopting such the plating method.
In accordance with the first feature of the invention, it is characterized by a plating method comprising the steps of dipping an object to be processed and an electrode plate into a solution containing designated metal ions; allowing a forward current to flow through the object and the electrode thereby to form a metal film originated from the designated metal ions on the object; and allowing a backward current to flow through the object and the electrode thereby to remove a part of the metal film formed on the object. According to the above method, a part of excessive metal can be uniformly eliminated thereby to contribute to the planarization of the surface of the object.
In accordance with the second feature of the invention, it is characterized by a plating method comprising the steps of forming a superfluous amount of metal film on an object to be processed; dipping the object and an electrode plate into a solution containing metal ions as a base of the metal film; and allowing a designated backward current to flow through the object and the electrode thereby to remove a part of the metal film formed on the object. Also in this method, since the part of excessive metal can be eliminated uniformly, it is possible to contribute to the planarization of the surface of the object.
In accordance with the third feature of the invention, the forward current is characterized by an electrical current having its variable magnitude.
In accordance with the fourth feature of the invention, the backward current is characterized by an electrical current having its variable magnitude.
In accordance with the fifth feature of the invention, it is characterized by the above-mentioned plating method further comprising the steps of measuring the forward current; calculating a thickness of the metal film on the object by the forward current measured; and judging whether the thickness of the metal film is in excess of a designated thickness, wherein the removing step is initiated when it is judged at the judging step that the thickness of the metal film is in excess of the designated thickness.
In accordance with the sixth feature of the invention, the above plating method is characterized in that the metal is identical to copper and the object to be processed is a semiconductor wafer having contact holes.
In accordance with the seventh feature of the invention, the solution containing the metal ions is a solution containing at least sulfuric acid.
In accordance with the eighth feature of the invention, the solution containing the metal ions is a solution containing at least phosphoric acid.
In accordance with the ninth feature of the invention, the solution containing the metal ions is a solution containing at least acetic acid.
In accordance with the tenth feature of the invention, the solution containing the metal ions is a solution containing at least nitric acid.
In accordance with the eleventh feature of the invention, the solution containing the metal ions is a solution containing at least hydrochloric acid.
In accordance with the twelfth feature of the invention, the metal film formed on the object is removed to have one tenth of the thickness at the removing step, and the plating method further comprises the step of secondly removing a superfluous metal film on the object by executing a chemical mechanical polishing after finishing the removing step.
In accordance with the thirteenth feature of the invention, the above plating method further comprises the step of forming a barrier metal layer on the object to be processed.
In accordance with the fourteenth feature of the invention, the above plating method further comprises the step of forming a seed layer on the object to be processed.
In accordance with the fifteenth feature of the invention, the above plating method further comprises the step of allowing the backward current to flow through the object and the electrode plate thereby to remove a part of the barrier metal layer formed on the object.
In accordance with the sixteenth feature of the invention, it is characterized by a plating device for plating an object to be processed, comprising a cell allowing the object and an electrode plate to be dipped therein, the cell being capable of accommodating a solution containing designated metal ions for plating; a switch for connecting the object and the electrode plate to a desired polarity of a power source of direct current; and a control unit for controlling the switch in a manner that a forward current flows through the object and the electrode in case of forming a metal film originated from the designated metal ions on the object, while a backward current flows through the object and the electrode in case of removing a surplus of the metal film formed on the object. This plating device allows the backward current to flow in case of removing the superfluous metal film.
In accordance with the seventeenth feature of the invention, it is characterized by a plating system comprising a transporting device for transporting an object to be processed; a plating device for applying a plating process on the object; and a cleaning device for washing and cleaning the object subjected to the plating process. Also in this plating system, the plating device includes a cell allowing the object and an electrode plate to be dipped therein, the cell being capable of accommodating a solution containing designated metal ions for plating; a switch for connecting the object and the electrode plate to a desired polarity of a power source of direct current; and a control unit for controlling the switch in a manner that a forward current flows through the object and the electrode in case of forming a metal film originated from the designated metal ions on the object, while a backward current flows through the object and the electrode in case of removing a surplus of the metal film formed on the object. The plating system has an operation similar to that of the above plating device.
In accordance with the eighteenth feature of the invention, the plating system further comprises a barrier metal etching bath for removing the barrier metal layer from the object.
In accordance with the nineteenth feature of the invention, the plating system further comprises a device having a function to measure a film thickness of a plating layer.
In accordance with the twentieth feature of the invention, the plating system further comprises an annealing device for performing an annealing process.